The present invention relates to a combined power plant using a gas turbine, one or all of hot parts of which are cooled with steam and, more particularly, to a combined power plant having a gas turbine cooling duty steam supply system incorporated therein.
The present invention relates to a combined power plant using a gas turbine, one or all of hot parts of which are cooled with steam and, more particularly, to a combined power plant having a gas turbine cooling duty steam supply system incorporated therein.
Conventional heat recovery combined power plants using steam-cooled gas turbines, the hot part of which are cooled with steam, are known in which in view of the conditions of flow rate, pressure and temperature of the steam, at least a part of low temperature reheat steam exhausted from a high pressure steam turbine and an intermediate pressure steam generated in a heat recovery steam generator are supplied. The gas turbine cooling duty steam superheated by cooling is recovered into a high temperature reheat line. Prior art relating to this kind of combining power plant is shown, for example, in U.S. Pat. No. 5,577,377.
In U.S. Pat. No. 5,577,377, as a supply source of gas turbine cooling duty steam, in addition to the low temperature reheat steam and intermediate pressure steam, high pressure steam and high pressure primary superheater outlet steam also are used, which are high in temperature and generated in a heat recovery steam generator before steam is introduced into a steam turbine during start-up of the plant, that is, when low temperature steam is not exhausted from a high pressure steam turbine.
In this kind of combined power plant, usually, the above-mentioned conditions of flow rate, pressure and temperature necessary for the gas turbine cooling duty steam for cooling the hot parts of a gas turbine are determined for each gas turbine load in dependence on conditions of the gas turbine high temperature portions.
In a case where start-up and stop, or, load up and load down, of the plant are operated, the flow rate and pressure of the gas turbine cooling duty steam can be relatively easily regulated to the gas turbine cooling duty steam conditions corresponding to gas turbine loads by regulating valve control. As for the temperature of the gas turbine cooling duty steam, however, when the gas turbine cooling duty steam supply source in normal operation is only low temperature reheat steam and intermediate pressure steam, there is a problem that time delay occurs when the gas turbine cooling duty steam temperature changes according to a change in the gas turbine load and the temperature conditions necessary for the gas turbine cooling duty steam are not satisfied because of thermal transfer between piping for steam and the steam.
An object of the invention is to supply gas turbine cooling duty steam the temperature of which is within an allowable temperature range of the gas turbine cooling duty steam required for each gas turbine load set for safety operation of a steam-cooled gas turbine even in time of start-up and stop, or, load up and load down, of the plant.
In order to achieve the above object, a temperature lower limit setting means is provided for setting a lower limit of an allowable temperature range of gas turbine cooling duty steam for each load. When the gas turbine cooling duty steam becomes lower then the allowable temperature range of gas turbine cooling duty steam for a certain turbine load, high temperature steam is used for the gas turbine cooling duty steam to raise the gas turbine cooling duty steam temperature.
Further, a temperature lower limit setting means for setting a lower limit of an allowable temperature range of gas turbine cooling duty steam for each load and a cooling duty steam temperature rise control means provided with a temperature judging means for comparing the gas turbine cooling duty steam temperature and the lower limit of the allowable temperature range are provided. Since the allowable temperature range of the gas turbine cooling duty steam rises as a gas turbine load goes up, when the gas turbine cooling duty steam temperature is estimated to become lower than the allowable temperature range during a rise in the gas turbine load, a part of the high temperature high pressure steam is supplied as a part of the gas turbine cooling duty steam prior to load up of the gas turbine. During the gas turbine load up, the gas turbine cooling duty steam is raised in temperature until the gas turbine cooling duty steam temperature reaches a temperature within the allowable temperature range, and then gas turbine load up is effected.
Further, a temperature upper limit setting means is provided for setting an upper limit of an allowable temperature range of gas turbine cooling duty steam for each load, and when the gas turbine cooling duty steam is higher in temperature than the upper limit of the allowable temperature range, low temperature steam is used for the gas turbine cooling duty steam to lower the gas turbine cooling duty steam temperature.
Further, a temperature upper limit setting means for setting an upper limit of an allowable temperature range of gas turbine cooling duty steam for each load and a cooling duty steam temperature down control means provided with temperature judging means for comparing the gas turbine cooling duty steam temperature and the upper limit of the allowable temperature range are provided. Since the allowable temperature range of the gas turbine cooling duty steam is lowered as the gas turbine load goes down, when the gas turbine cooling duty steam temperature is estimated to become higher than the allowable temperature range during gas turbine load down, a part of the high pressure primary superheater outlet steam is supplied as a part of the gas turbine cooling duty steam prior to the gas turbine load down. When lowering the gas turbine load, the gas turbine cooling duty steam temperature is lowered until the gas turbine cooling duty steam temperature reaches a temperature within the allowable temperature range, and then the gas turbine load down is effected.
Further, a temperature upper limit setting means is provided for setting an upper limit of an allowable temperature range of gas turbine cooling duty steam for each load. When the gas turbine cooling duty steam temperature is higher than the upper limit of the allowable temperature range, a part or all of the high pressure primary superheater outlet steam is caused to bypass the high pressure secondary superheater to lower the high pressure steam temperature and the supply low temperature reheat steam lowered in temperature to the gas turbine hot parts, thereby to lower the gas turbine cooling duty steam temperature and supply gas turbine cooling duty steam, the temperature of which is within the allowable temperature range.
Further, a temperature upper limit setting means for setting an upper limit of an allowable temperature range of gas turbine cooling duty steam for each load and a cooling duty steam temperature down control means provided with temperature judging means for comparing the gas turbine cooling duty steam temperature and the upper limit of the allowable temperature range are provided. Since the allowable temperature range lowers as the gas turbine load goes down, when the gas turbine cooling duty steam temperature is higher than the upper limit of the allowable temperature range at the time of gas turbine load down, a part or all of the high pressure primary superheater outlet steam is caused to bypass the high pressure secondary superheater to lower the high pressure steam temperature prior to the gas turbine load down and to supply the low temperature reheat steam lowered in temperature to the gas turbine hot parts. Thus, the gas turbine cooling duty steam temperature is lowered at time of gas turbine load down until the gas turbine cooling duty steam temperature reaches a temperature within the allowable temperature range and then the gas turbine load down is effected.